Many potentiometers are known in the field of electrical controls. Some of these are intended for use on a control panel as an externally accessible control. These controls are designed for repeated adjustment--usually through a rotable drive shaft on which a control knob is mounted--and are rated in some instances for one million operations.
Another type of potentiometer is a trimming potentiometer. This type of device is intended for mounting on a circuit board, or other supporting surface, which is usually housed within an item of electrical apparatus. This type of control is generally set at the beginning of its life, and in some instances, is only readjusted during its life when the circuit is serviced. Trimming potentiometers may be multi-turn or single-turn, and open-frame, partially open-frame, or sealed. Such devices may be used as rheostats by connecting two terminals, a fixed terminal and another terminal that is connected to an adjustable wiper contact, in series in an electrical circuit.
The competing considerations in the manufacture of a trimming potentiometer are cost versus the specification requirements for the device. At one end of this cost spectrum are high-cost devices that are designed to meet stringent military specifications. At the other end of the spectrum are low-cost devices which satisfy a particular commercial demand.
One way of reducing manufacturing costs is reducing the number of parts required to make a trimming potentiometer. Another way of reducing these costs is providing a structure that requires a small number of inexpensive manufacturing and assembly steps.
In Falco, U.S. Pat. No. 3,772,630, issued Nov. 13, 1973, a potentiometer that is presented as simple and inexpensive includes a base with a resistance track mounted thereon, a collector having an annular portion, and three connecting tags. One tag is electrically connected to the collector, and the other two tags are connected to the opposite ends of the resistance track. A slider is rotatably mounted on the annular portion of the collector and has a stud for contacting the resistance track.
In Bang, et al., U.S. Pat. No. 3,448,428, issued June 3, 1969, metal tags or terminal pins are made unnecessary by coating tongues extending from a rectangular base with either a resistive material or a metal plating material. The collector is formed either as a track on the opposite side of the base from the resistance element, or as a plate disposed within a housing with the base. Where a collector track is formed, a rotatable shaft is journaled through the base and carries a wiper contact finger on each side of the base with contacts engaging the resistance element on one side and the collector track on the other side. Where a housing is included in the structure, the wiper contact is more intricately mounted.
While these prior art devices strive for simplified and less expensive construction, it should be apparent from the following description that those objects are more readily obtained with a device as described herein.